This invention generally relates to formulations of drugs, especially drugs having low solubility, and more particularly to methods of making formulations of such drugs to enhance their rate of dissolution.
The bioavailability of a drug can be limited by poor dissolution of the drug into aqueous bodily fluids following administration. This rate-limiting step may therefore be critical to rapidly attaining therapeutically effective drug levels.
Traditional approaches to parenteral delivery of poorly soluble drugs include using large volumes of aqueous diluents, solubilizing agents, detergents, non-aqueous solvents, or non-physiological pH solutions. These formulations, however, can increase the systemic toxicity of the drug composition or damage body tissues at the site of administration.
Other approaches have focused on the physical form of the drug itself. Since the dissolution rate of a drug particle is directly related to its surface area available to contact the aqueous media at the site of administration or site of absorption, methods of preparing drugs in nanoparticulate form have been developed in an effort to maximize the drug surface area, as described, for example, in U.S. Pat. No. 5,534,270 to De Castro and U.S. Pat. No. 5,587,143 to Wong. Nanoparticles however, can be difficult to produce and maintain in a stable form due to the tendency of the nanoparticles to flocculate or agglomerate, particularly without the presence of surface modifying agents adsorbed or coated onto the particles. Furthermore, milling or wet grinding techniques, which are typically employed for nanonization, can be undesirable, as it can take several days to process a single batch, scaling-up of the milling or grinding process can be difficult and/or costly, the process can be difficult to conduct aseptically, and it is difficult to eliminate shedding of milling media into the product.
Other efforts directed at enhancing the rate of dissolution have focused on delivering the drug as a dispersion in a water-soluble or biodegradable matrix, typically in the form of polymeric microparticles. For example, the dissolution rate of dexamethasone reportedly was improved by entrapping the drug in chitosan microspheres made by spray-drying (Genta, et al., S.T.P. Pharma Sciences 5(3):202-07 (1995)). Similarly, others have reported enhanced dissolution rates by mixing a poorly soluble drug powder with a water-soluble gelatin, which purportedly makes the surface of the drug hydrophilic (Imai, et al., J. Pharm. Pharmacol, 42:615-19(1990)).
Related efforts have been directed to forming relatively large, porous matrices of low solubility drugs. For example, Roland and Paeratakul, xe2x80x9cSpherical Agglomerates of Water-Insoluble Drugs,xe2x80x9d J. Pharma. Sci., 78(1 1):964-67 (1989) discloses preparing beads having a low solubility drug content up to 98%, wherein the beads have a porous internal structure. Such large beads, however, are unsuitable for parenteral administration, and the beads have less surface area and slower dissolution rates than smaller particles.
It is therefore an object of the present invention to provide compositions enhancing the dissolution rate of drugs, especially drugs having low aqueous solubility, and to provide methods of making such compositions.
It is another object of the present invention to provide compositions providing enhanced dissolution of drugs, especially drugs of low aqueous solubility, in a formulation suitable for administration by a variety of routes, including, but not limited to, parenteral, mucosal, oral, and topical administration, for local, regional, or systemic effect.
It is further object of the present invention to provide compositions for administration as a bolus injection instead of by infusion.
Drugs are provided in a porous matrix form wherein the dissolution rate of the drug is enhanced when the matrix is contacted with an aqueous medium. In a preferred embodiment, low aqueous solubility drugs are provided in a porous matrix form which forms microparticles when the matrix is contacted with an aqueous medium. The porous matrix with low aqueous solubility drugs yields upon contact with an aqueous medium microparticles having a mean diameter between about 0.1 and 5 xcexcm and a total surface area greater than about 0.9 m2/mL. The dry porous matrix is in a dry powder form having a TAP density less than or equal to 1.0 g/mL and/or having a total surface area (sum of internal and external surface area) of greater than or equal to 0.2 m2/g. The porous matrices that contain the drug are preferably made using a process that includes (i) dissolving a drug in a volatile solvent to form a drug solution, (ii) combining at least one pore forming agent with the drug solution to form an emulsion, suspension, or second solution, and (iii) removing the volatile solvent and pore forming agent from the emulsion, suspension, or second solution to yield the dry porous matrix of drug. The resulting porous matrix has a faster rate of dissolution following administration to a patient, as compared to nonporous matrix forms of the drug. The pore forming agent can be either a volatile liquid that is immiscible with the drug solvent or a volatile solid compound, preferably a volatile salt. If the pore forming agent is a liquid, the agent is emulsified with the drug solution. If the pore forming agent is a solid, the agent is (i) dissolved in the drug solution, (ii) dissolved in a solvent that is not miscible in tile drug solvent and then emulsified with the drug solution, or (iii) suspended as solid particulates in the drug solution. Optionally, hydrophilic excipients, wetting agents, and/or tonicity agents mall be added to the drug solvent, the pore forming agent solvent, or both. The solution, emulsion, or suspension of the pore forming agent in the drug solution is then processed to remove the drug solvent and the pore forming agent, as well as any pore forming agent solvent. In a preferred embodiment, spray drying, optionally followed by lyophilization, fluid bed drying, or vacuum drying, is used to remove the solvents and the pore forming agent.
An advantage of the formulations is that they can be administered as a bolus, when the drug normally must be infused to avoid precipitation of the drug. By avoiding precipitation of drug in vivo, the formulations can also be administered parenterally. An additional advantage is the formulations can be administered in reduced volumes.
In one embodiment, the matrix further includes a pegylated excipient, such as pegylated phospholipid, with the drug. The pegylated excipient shields the drug from macrophage uptake, which prolong its half-life or enhance bioavailability of the drug.
In a preferred embodiment, the porous drug matrix is reconstituted with an aqueous medium and administered parenterally, such as intramuscularly, subcutaneously, or intravenously. Alternatively, the porous drug matrix can be further processed using standard techniques into tablets or capsules for oral administration or into rectal suppositories, delivered using a dry powder inhaler for pulmonary administration, or mixed/processed into a cream or ointment for topical administration.